1Department of Neurosurgery, Virginia Commonwealth University School of Medicine, Richmond, VA 23298, USA2Department of Internal Medicine, University of Illinois College of Medicine at Urbana-Champaign, Urbana, IL 61801, USA3University of Illinois College of Medicine at Urbana-Champaign, Urbana, IL 61801, USA4Department of Neurosurgery, University of Illinois College of Medicine at Urbana-Champaign, Carle Foundation Hospital, 602 West University Avenue, Urbana, IL 61801, USA

Received 24 September 2013; Accepted 10 October 2013; Published 12 January 2014